Short-period Components Research Articles

Erratum

Table 3 in the report "Latitudinal and longitudinal oscillations of cloud features on Neptune" by Lawrence A. Sromovsky (1 Nov., p. 684) contained errors. In column 4, the two values for inferred shear should have been -0.8 and -13.8 m/(s-deg), respectively. The corresponding text in column 1 on page 686 should have read, "the advection model is quantitatively upheld for the DS2 motions, but not for the short-period component of the GDS motions. They both agree on phase lags, although the GDS is not in good quantitative agreement on amplitudes. Relative to a smooth shear profile obtained from a simple polynomial fit to the observed wind speeds as a function of latitude (11), the shear derived from the advective model amplitude ratio is almost the same for DS2, but a ninth as large for the GDS."

Erratum: Latitudinal and Longitudinal Oscillations of Cloud Features on Neptune

Table 3 in the report "Latitudinal and longitudinal oscillations of cloud features on Neptune" by Lawrence A. Sromovsky (1 Nov., p. 684) contained errors. In column 4, the two values for inferred shear should have been –0.8 and –13.8 m/(s-deg), respectively. The corresponding text in column 1 on page 686 should have read, "the advection model is quantitatively upheld for the DS2 motions, but not for the short-period component of the GDS motions. They both agree on phase lags, although the GDS is not in good quantitative agreement on amplitudes. Relative to a smooth shear profile obtained from a simple polynomial fit to the observed wind speeds as a function of latitude ( 11 ), the shear derived from the advective model amplitude ratio is almost the same for DS2, but a ninth as large for the GDS."

Globally Coordinated Magnetic Observations Along 210.DEG. Magnetic Meridian during STEP Period: 1. Preliminary Results of Low-Latitude Pc 3's.

The Solar-Terrestrial Environment Laboratory (STEL), Nagoya University, is carrying out multinationally coordinated magnetic observations along the 210° magnetic meridian from high latitudes, through middle and low latitudes, to the equatorial region, spanning L=9.05-1.03, in cooperation with 14 institutes in Japan, Australia, USA, and Russia during the STEP period of 1990-1997. In this paper, we introduce in detail the project of global magnetic observations along the 210° magnetic meridian, and illustrate preliminary results of power spectrum and cross correlation analysis of low-latitude pulsations at the 6 chain stations installed in 1990.The results can be summarized as follows: (1) There are two spectral peaks in the Pc 3 range. A shorter-period component in the 10-20sec range exhibits standing field-line resonance behavior around L=1.58, while the longer-period component in the 20-50sec range indicates three different characters, a standing field-line oscillation at L>2.1, a second-harmonic cavity resonance oscillation in the plasmasphere, and propagating-mode waves with phase delays from lower to higher latitudes. (2) An ssc with δH-215nT magnitude at L=1.22 on March 24, 1991, was found to stimulate cavity-mode Pc 3 pulsations with duration <20min and identical 15.5 and 25.3mHz frequencies over the L=1.14-2.13 low-latitude region.

Very-High-Eccentricity Librations at Some Higher Order Resonances

Motions near the 3:1, 4:1 and 5:2 resonances with Jupiter are studied by means of numerical integrations of a semi-analytically averaged Sun-Jupiter-asteroid planar problem. In order to have a model including the very-high-eccentricity regions of the phase space, we adopted a set of local expansions of the disturbing potential, adequate to perform the numerical exploration of regions in the phase space with eccentricities higher than 0.9 (Ferraz-Mello and Klafke, 1991). Individual solutions and qualitative results thus obtained are completely reproduced by numerical integration of the complete equations by filtering off the short-period components of these solutions.

Mutual interactions between optic lobe circadian pacemakers in the cricket Gryllus bimaculatus

The coupling mechanism between the bilaterally paired optic lobe circadian pacemakers in the cricket Gryllus bimaculatus was investigated by recording locomotor activity, under constant light or constant red light, after the optic nerve was unilaterally severed. 1. The majority (about 70%) of the animals showed a locomotor rhythm with 2 rhythmic components; one freerunning with a period of 25.33 ± 0.41 (SD) h and the other with 24.36 ± 0.37 (SD) h under constant light (Fig. 3A). 2. Removal of the intact side optic lobe abolished the longer period component (Fig. 4A), while the operation on the operated side caused a reverse effect (Fig. 4B), indicating that the longer and the shorter period components are driven by the pacemaker on the intact and the operated side, respectively. 3. The activity driven by a pacemaker was inhibited during the subjective day of the contralateral pacemaker (circadian time 0–10, Fig. 5). 4. The freerunning periods of the two components were not constant but varied as a function of the mutual phase angle relationship (Figs. 3A, 7, 8).

Observations of fuors. II. Light curve of V 1515 Cyg and fourier analysis of the short-period component

Observations of fuors. II. Light curve of V 1515 Cyg and fourier analysis of the short-period component

LONG-PERIOD RADIAL-VELOCITY VARIATIONS OF ARCTURUS

ABSTRACT Precise measurements of the radial velocity of Arcturus were obtained on 43 occasions between 1981 and 1985. The measurements show a 500 m/s range, confirming the radial velocity variability of Arcturus. Multiperiod models which give a good representation of the velocities are derived using a least-squares technique. The models also fit the velocities of Smith et al. (1987). It is suggested that the small-amplitude short-period components of the models could be analogous to the solar five-minute oscillations. The best-fitting models require the largest-amplitude component to have a period of at least 640 days.

Manifestations of short-period electric field fluctuations in the equatorial lower thermosphere

Measurements (≏90h) of phase path, P of lower F-region (∼ 200km) reflections at normal incidence over Kodaikanal (dip 3.0°N) revealed the time rate of change of phase path, Ṗ (Doppler frequency shift, Δf) to undergo quasi-periodic fluctuations quite regularly during the day time. The changes in Ṗ which have peak-to-peak amplitudes of 6 to 30 ms−1 (0.1-0.5Hz in Δf) exhibit quasi-periods in the band 60-600s, comprising of two overlapping spectral domains: the shorter-period components (T < 240s) and the longer-period components (T > 300s). The spectral content of the variations in Ṗ is found to depend on the ambient equatorial electrojet strength and associated ionospheric conditions in that, while the longerperiod components persist almost all the time, the shorter-period components tend to cease during the times of disappearance of equatorial sporadic-E (Esq) on ionograms (partial counter-electrojet). Perturbations in the F-region vertical plasma drift, VzF are considered to be primarily responsible for the observed changes in Ṗ, particularly the longer-period (T > 300s) fluctuations. Correlative and visual studies of the simultaneous data (≏ 52h) of phase path at Kodaikanal and of ground level geomagnetic micropulsations at Trivandrum (located similar 200km south of Kodaikanal, dip 0.6°S) showed the absence of a persistent and clear-cut association of the fluctuations in Ṗ with Pc4/Pc5 micropulsations, indicating that hydromagnetic waves are not a primary source of the VzF pulsations. It is suggested that the longer-period (300 < T < 600s) fluctuations in VzF are due to gravity waves related changes in the east-west electric field at E-region altitudes outside the electrojet belt, and mapped along the field lines to F-region levels over Kodaikanal.

Distribution of maximum water levels due to the Japan Sea Tsunami on 26 May 1983

By measuring the maximum water level of the traces attained by the Japan Sea Tsunami on 26 May 1983, we obtained the distribution along the west coast of the northeast Japan. The level reaches a maximum at the coast eastward of the epicenter and decreases with the relationship 8.6e −0.017x(m) with distancex (km) measured from the coast nearest to the epicenter. A small increase of levels was observed at coasts to the south of the tsunami source having distance larger than 200 km. With the aid of tide gauge records we revealed an excitation of edge wave which brought about the small increase of levels at the southern coast. In comparison with the decrease with distance obtained on the coasts of the main islands of Japan, some noticeable peaks were observed at several small islands. It is suggested that the reason why a short period component is predominant for the initial wave motion of tsunami is that the source region has depth of 3, 000 meters. The feature of wave period is discussed in comparison with that of the 1964 Niigata Tsunami.

Slow-wave oscillations of the multi-unit activity average frequency in the human brain during drowsiness and sleep

Slow-wave oscillations of the mean frequency of multi-unit activity (MUA) were studied in the cerebral subcortical structures of parkinsonic and epileptic patients treated with the aid of implanted electrodes, during sleep, drowsiness and awakening. During slow-wave sleep, the MUA slow-wave oscillations become augmented, the number of oscillatory components increases as well as the amount of oscillations with identical or similar periods in different structures. During paradoxical sleep, the total amount of oscillatory components decreases. The MUA rhythmic activity is quite obvious in awakening from sleep, the short-period components prevailing. The data obtained reveal high incidence of the rhythms with periods of about 20 sec which is considered from the standpoint of the hypothetical adaptogenic rhythm in the CNS developing at the moments of certain efforts and adaptive activity of the organism.

Long‐term variations of the external and internal components of the Earth's magnetic field

The present study applies classical techniques of time series analysis to the separation of the external and internal signals from the geomagnetic field. We first differentiate the data with respect to time in order to get rid of the large secular variation over the long time span considered (up to 100 years). Next we filter the resulting data to eliminate short‐period components of the magnetic signals. We then proceed to identify the external signal by comparing the long‐term variations of the processed components of the geomagnetic field, as measured at different European observatories, with the long‐term variations of geomagnetic indices devised to characterize the fields from external sources. Finally, we remove the identified external signal from the geomagnetic field series and get a satisfactory estimate of the internal signal. This procedure is facilitated by the different behaviors of the two signals over the considered time span. The external signal is inherently of recurrent nature linked to solar‐terrestrial interaction; it oscillates around zero with a maximum amplitude of about 5 nT/yr. The internal signal, on the other hand, displays the characteristics of a secular trend, combining sustained monotonous behavior over periods of several decades with sudden slope variations and reversals; the total range of this internal secular signal is of the order of 50 nT/yr, far larger than any external contribution. Using the 1883–1983 magnetic series at Chambon‐la‐Forêt, the 1890–1983 series at Niemegk, and shorter series at the United Kingdom observatories of Eskdalemuir and Hartland, we have been able to get a coherent overall picture of the secular variation as measured in Europe. For instance, the first‐order time derivative of the Y (east) component essentially displays an increase in two steps from 1900 to 1925, a monotonous decrease from 1925 to 1969 with a regular steplike substructure, and a rapid increase since 1969, followed by a marked reversal of slope in 1979. These results emphasize the internal origin of the 1969 jerk and single out, in Europe, a 1979 event of opposite sign, these two features being quite reminiscent of the behavior of the secular variation during the first quarter of the century.

An undulator with a composite magnetic field

A new type of undulator greatly improved in tunability as compared with a usual undulator, is proposed. The undulator has a composite magnetic field which is a linear superposition of two sinusoidally varying fields with different spatial periods. The wavelength can be changed by varying the field strength of the longer-period component while keeping that of the shorter-period component at the highest possible value. Numerical calculations of the spectral brightness were carried out. The proper ratios between the two spatial periods were found to be 3:1, 5:1 and 7:1.

Evaluation of kinematic interaction of soil-foundation systems by a stochastic model

At the present practice, the earthquake response analysis of structures is generally based on an assumption that the ground just beneath a foundation vibrates in the same phase and with the same amplitude everywhere. However, it is very doubtful that a structure vibrates as if it were set on a shaking table. As the foundation slab, which is relatively stiff compared with the soil, works to constrain such ground motions, short period components of the ground motions whose wave length is short to the dimension of the slab are naturally weakened. Consequently the slab has the effect of a kind of low pass filter on the ground motions. This effect is called ‘kinematic interaction’. 1 In the past, many studies have been made on the kinematic interaction both theoretically and experimentally, 2–9 and characteristics of the kinematic interaction have become clearer. However, since the effect of kinematic interaction is so complicated to depend totally on a geometrical pattern of a foundation slab, ground characteristics and the excitation, further researches are needed for incorporation of the effect into dynamic design practice. This paper formulates the kinematic interaction of embedded rectangular foundations by the random vibration theory, and discusses the effect by examining field data obtained in earthquakes. Since the formulation is based on the fact that statistical correlation of ground motions at different points decreases as the distance between the different points increase, and especially when components of high frequency are contained in ground motions, characteristics of mutual correlations of the motions of different points are first investigated. Next, the formulation of the kinematic interaction is investigated. In order to justify a low pass filter by this stochastic model, earthquake records observed at a large scale inground tank and a foundation, whose material is cement-mixed soil-improved-ground, are analysed as examples of deep and shallow embedded foundations respectively. Also the filtering effect on microtermor records observed at a reinforced concrete four-storey school building are investigated as another example of more general structures.

Broad-band deconvolution of GDSN data

Summary Advances in the theory of wave propagation and source mechanism have coincided with the recent deployment of a global network of digitally recording seismographs, the GDSN (Global Digital Seismograph Network). We demonstrate that broad-band records of body-wave ground displacement and velocity with spectral information from several hertz to tens of seconds can be obtained by the simultaneous deconvolution of the long- and short-period components of the GDSN seismographs. Frequency-dependent effects in body waves that may arise from source complexity or from propagation through the Earth are much more apparent and measurable in the broad-band records than in the original seismograms.

Rayleigh wave synthetic seismograms from multi-dimensional simulations of underground explosions

abstractA general method is presented for coupling the near-source wave fields, obtained from time-stepping numerical calculations, with analytically formulated methods for continuing the wave field to larger ranges. The source calculation may include a free surface and other material boundaries as well as arbitrary material behavior, as long as it is carried into a region where the material response is linearly elastic. The method, which is based on an elastodynamic representation theorem, is worked out in detail for the Rayleigh wave modes for an axisymmetric source in a plane-layered earth model and is demonstrated by a sample calculation for which the exact solution is known.Two realistic, axisymmetric simulations of nuclear explosions (20 and 150 kt at 1-km depth) are studied to estimate the effect of nonlinear interactions with the free surface on the far-field Rayleigh waves. The importance of these two-dimensional phenomena is quantified by comparing far-field Rayleigh waves computed from these simulations with Rayleigh waves computed from analogous one-dimensional (spherically symmetric) simulations. While the two-dimensional simulations exhibit substantial spallation associated with the free surface, the predicted effect on the Rayleigh wave peak amplitudes is negligible. Two-dimensional effects also alter the waveform very little, apart from some enhancement of very short-period components for the larger explosion.

Period analysis of the Piccardi P test

Abstract The Piccardi P test is a method to evaluate the difference between the sedimentation rate of a colloid under a copper screen and in open air. Three different sets of daily test values, collected in Florence in the period 1955–1972, have been considered. Each set has been analyzed with a 5 component Fourier expansion, varying the T period of the maximum component between 6 and 300 months. The best agreement between experimental and theoretical data has been obtained for T = 12 years. Repeating the computation with a 10 component expansion, this value is modified to T = 22.5 years, and another optimum fit at T = 24 years. Those results confirm the Piccardi hypothesis about the connection between the solar cycle and the P test trend. Further confirmation has been obtained by comparing the Wolf sunspot number trend for the period 1954–1974 with the T values obtained by separately analyzing the periods 1955–1966 and 1966–1972. Amore detailed analysis of the short period components stresses the importa...

On the generation of satellite position (and velocity) by a mixed analytical-numerical procedure

The generation of accurate Earth-satellite ephemerides by numerical integration, over a period of perhaps weeks, can consume an inordinate amount of computer time. No satisfactory purely analytical procedure exists, but if short-period components of the standard elliptic elements are removed analytically, the resulting mean elements can be integrated with a step time that is longer than the satellite's orbital period. The definition of the mean elements depends on the particular perturbations included in the orbit generator and regarded as non-resonant. It is best if short-period perturbations are not applied to the orbital elements themselves but to the satellite's position (and velocity if required), expressed in a system of cylindrical polar coordinates, and the paper shows how mean elements can be recovered from position and velocity. A computer program has been written to test the proposed procedure for generating ephemerides, using a truncated potential field. Some results from this program are presented.

On the fine structure of equatorial Pi2 pulsations.

The irregular pulsations of Pi2 class are reported to contain most often pulsations of shorter periods in the range of Pils, probably forming the fine structure of Pi2 pulsations. The properties of such short period pulsations are studied utilizing the data obtained during 1967-74 at Choutuppal (geomagnetic latitude: 7°28′N), India. The study reveals a clear influence of background magnetic activity on the occurrence of shorter period components, an appreciable seasonal dependence of fine structure activity and a systematic change in the nature of this dependence during the course of a Solar Cycle, in that the equinoxial season predominates in the fine structure activity during years around sunspot maximum, while during years away from solar maximum the activity is more pronounced during winter season. The period distribution of short period activity from a detailed power spectral analysis revealed clear peaks around 5.5, 11.0, and 16.5sec. It is suggested that at least part of the equatorial Pi2 fine structure, particularly the signals with periods around 10.0sec and more be viewed as due to resonance of innermost cavity of magnetosphere, triggered by the impulsive disturbances generated at the boundary or outside of the magnetosphere.

Estimations of short-period accelerations, velocities and displacements due to a fault model.

The present fault model available in the field of seismology is the highcut source model. Since detailed behaviors of short-period components at the source are still unknown, it is quite difficult to reproduce observed accelerations (or Intensities) by modelling the earthquake source. In this paper, applying a low-pass filter to observed strong-motion accelerograms in the frequency range from O Hz to ν Hz, relations between maximum amplitudes and cutoff period T (=1/ν) are obtained. The empirical equations for maximum acceleration, um (gal), maximum velocity, um (kine), and maximum displacement, um (cm), as a function of T (sec) are found to be and If values at T=T0 are known, maximum values for short periods, for in-stance at T=0.1sec, can be estimated. For dislocation source models corresponding to M=5 to 8, theoretical seismograms are computed. The above cutoff period is defined as the period at which the spectral amplitude is equal to or less than 1/1, 000 of the maximum value and maximum short-period accelerations at T=0.1sec are estimated by using the above empirical relations. Although, in this study, only an infinite medium is considered and expected accelerations at prescribed stations computed by using I-R relations of SHIMA (1977) have large variations, it can be said that maximum accelerations obtained for the present fault models give plausible values. In the present paper, possibility is only investigated whether the fault model, assuming the simple infinite medium, can realize or not the shortperiod maximum accelerations we experience during the earthquake. It is quite important to study spatial distributions of maximum accelerations as well as maximum velocities in the period range, which bring about great damage in the epicentral area, by adopting a pertinent hypothetical earthquake model and taking more realistic multi-layered surface structures into account.

Long-period surface velocities and accelerations due to a dislocation source model in a medium with superficial multi-layers. II.

The formulation derived in Part I of this paper, to obtain disturbances at a surface of a medium with superficial multi-layers due to a dimensional fault is revised by taking surface wave contributions approximately into consideration.Surface accelerations due to a simple source model with source time function of ramp type are found to be too small, even if our interest in the present study is on rather long-period components. One possibility is shown that rather large accelerations are obtained by adopting different source time functions from the simple ramp type, keeping other focal factors the same as in the presently available fault model.Accelerations thus obtained are of course only tentative and their absolute values cannot be discussed at the present stage of seismology. However, if surface structures at many places are clarified and detailed behaviors of short-period components in the source time function, especially for large earthquakes, are elucidated, then the present formulation may make it possible to discuss even absolute values of accelerations.